View Full Version : Star Classifications

2004-Sep-06, 03:04 AM
I often hear stars reffered to as a something class star- for example, our sun is a G class star (I think... :unsure:). What are the different classes and what do they mean?

2004-Sep-06, 03:26 AM
The different classes are OBAFGKM. I remember them by saying, "Oh boy, a fat guy kissed me." Here is an HR diagram (http://ast.star.rl.ac.uk/hr.html) They are classified by temp.

This one (http://www.astro.sunysb.edu/fwalter/AST248/spt.html) tells you more about each spectral classification. I don't think the OBA... stand for any particular word.

2004-Sep-06, 04:21 AM
If you're a guy, it's: Oh Boy, A Fat Girl Kissed Me! :lol:

2004-Sep-06, 04:47 AM
Luminosity classes (http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml).

Also there are little suffixes, p and s and c for things like Perculiar and Strange and Carbon.

There are others, like flare stars, methane Dwarfs.

Another set of classifications follows the star where a particular phenomena is first observed, for example Wolf-Rayet stars, Cepheid Variables, RR Liraes, I am still finding different types of stars, I haven't seen a complete list of these, this ( A DIGITAL SPECTRAL CLASSIFICATION ATLAS (http://nedwww.ipac.caltech.edu/level5/Gray/frames.html)) comes close though, but there are more.

I like this site Stars (http://www.astro.uiuc.edu/~kaler/sow/sowlist.html).


2004-Sep-07, 07:45 PM
Back in the early days, the spectral classifications were put in the order ABCDEFGHKLM, and O was a special case. This was basing it on which spectral lines showed up and how intense they were, and whether they were absorbsion or emission lines. It was eventually realized that if you sorted the stars by mass and temperature, and ignored the highly evolved [old] stars, it made more sense for the sequence to be OBAFGKM, and C, D, E, H, and L stars were not just rare missing links, but didn't really exist. We now use L to indicate Lithium burning Brown Dwarfs. The letters never stood for anything scientific as initial letters.

Tim Thompson
2004-Sep-08, 12:47 AM
The classification scheme was orignally developed by Annie Cannon, but the alphabetizing was done by Williamina Fleming, who used the hydrogen spectral lines as her guide. We now understand that, as a function of temperature, the original alphabetical order is wrong, hence the modern rearrangement of the letters (Spectral Classification (http://spiff.rit.edu/classes/phys440/lectures/spec_class/spec_class.html), from Michael Richmond (http://stupendous.rit.edu/richmond/index.html) and the Rochester Institute of Technology (http://www.rit.edu/old/) has good illustrative pictures).

The current scheme has been expanded to include the spectral type, luminosity class & peculiarity code (Note on spectral classification (http://cfa-www.harvard.edu/~pberlind/atlas/htmls/note.html) from the Harvard-Smisthonian Center for Astrophysics (http://cfa-www.harvard.edu/)).